Re: Upgrading a single controller to an active/active cluster.

I guess all of this sort of has to start with what you intend to do with the "second" controller. Have you bought additional disk shelves for a/the "second" controller? Are you planning to move CIFS/NFS shares over to the "second" controller?

Anyway, attaching the existing shelves to one of the controllers isn't any different than any other upgrade. One needs basically the same ONTap version and a new install on the root volume after things first come up. Disks need to be assigned to the new controller head during the first boot up and one probably should run a diag kernel before even getting that far.

How you intend on splitting up your shelves or using the second controller depends a lot on what you intend to do with that second controller. Assigning a couple of disks for a quick raid4 root aggregate+volume for the new controller isn't really that big of an issue, but it is sort of non-standard. Even if software disk ownership is now the standard, the concept of keeping disk shelves sort of segregated physically via cabling is still the recommended norm (although I have seen some interesting variations that work).

So it all comes down to what you want to do first, then one can help you with the "how".